My question is will I need to use magnum primers with this load? Or any load with 300 Win Mag for that matter.

Thanks,
Scott

Twist rate for that rifle ? Mine is 1 in 11 and 74 grs of RL 22 is a 1/4 min load at 100 with groups at 700 displaying very little vertical and group size of 2.5 inches . Pretty windy that daybut steady ! This is with Lapua brass , fed 215gm primeers , 74 grs RL 22 and a 190 SMK . Running around 3050 as tested with a Oehler 35 with 8 ft screen spacing . Es below 20 and sd in single digits . I have used 190 gr wildcats with the samre results .